Beta-cyclohomocitral is a valuable substance useful in the formulation of perfumery, tobacco and food flavoring materials, as disclosed in copending application for U.S. Pat. No. 507,412 filed on Sept. 19, 1974.
The preparation of beta-cyclohomocitral and beta-ionone enol acetate (an intermediate for producing beta-cyclohomocitral is set forth in British Pat. No. 775,060, which discloses (A) first forming an iso-C.sub.11 -aldehyde by (i) condensing ethoxy-acetylene with 2,6,6-trimethylcyclohexanone-1, (ii) partially hydrogenating the resulting acetylenic carbinol so as to convert the triple bond therein into a double bond, and (iii) treating the resulting olefinic compound with an acid; then (B) reacting the resulting iso-C.sub.11 -aldehyde with acetic anhydride and fused sodium acetate under reflux conditions to form beta-ionone enol acetate; and (C) hydrolyzing the beta-ionone enol acetate with alcoholic base (sodium bicarbonate-methanol mixture) to form beta-cyclohomocitral. This multi-step sequence of reactions and the low yield of final product render the synthesis of British Pat. No. 775,060 commercially impractical.
Reactions of peracetic acid with .alpha.-aralkylidenecyclanones in the presence of buffer are disclosed by Walton J. Org. Chem., 22, 1161 (1957), for example: ##SPC2##
Wherein R is phenyl, substituted phenyl or 2-furyl and n is 3 or 4.
Broadly, the reaction of a system containing conjugated unsaturation with a peroxidation agent is known (See Wenkert and Rubin, Nature 170, 708 (1952) wherein the reaction of an alpha, beta-unsaturated ketone having a phenyl moiety in the beta position is oxidized to form an enol ester is taught) but reaction of an ionone type material with an oxidizing agent to form an acyloxyethylene moiety (as opposed to an epoxide moiety) has been heretofore unknown. Also see Boesken et al., Rec. Trav. Chim. 50, 827 (1931); 52, 874 (1933); 55, 786 (1936), who have shown that peroxyacetic acid reacts with benzalacetone and related ketones with the insertion of an oxygen atom between the carbonyl and styryl groups, resulting in the formation of enol esters of phenylacetaldehyde and benzyl ketones. A relevant reaction taught by Boeseken et al. is as follows: ##SPC3##
Wherein R.sub.1 and R.sub.2 are each hydrogen or methyl.
FMC Corporation "Preparation, Properties, Reactions and Uses of Organic Peracids and Their Salts" discloses methods for the preparation of peracetic acid, performic acid and perpropionic acid at pages 3-21 and discusses the use of peracids in carrying out Baeyer-Villiger oxidations of unsaturated ketones at pages 84-89.
The invention accordingly comprises the novel process and steps, specific embodiments of which are also described hereinafter by use of experiments and in accordance with what is now the preferred practice of the invention.
Briefly, the process of this invention comprises forming beta-cyclohomocitral by oxidizing beta-ionone with hydrogen peroxide in the presence of inorganic base in one step.
The strength of hydrogen peroxide used is from about 10 percent up to about 50 percent; preferably, 30 percent aqueous hydrogen peroxide. The inorganic base used may be an alkali metal hydroxide or alkali metal carbonate such as sodium carbonate, potassium carbonate, lithium carbonate, sodium hydroxide, potassium hydroxide or lithium hydroxide; preferably sodium hydroxide. The mole ratio of hydrogen peroxide:beta-ionone is preferably from about 1.1:1 up to about 3:1.
The process of our invention is specific to beta-ionone. As further exemplified infra, when the reaction conditions of our process are applied to alpha-ionone, as opposed to beta-ionone, epoxide formation occurs and no beta-cyclohomocitral is formed.
Example I serves to illustrate our invention as it is now preferred to practice it. Example VI following, serves to illustrate the unworkability of the process of our invention where dimethyl formamide is used in the oxidation reaction of beta-ionone with peracetic acid. Examples II-V illustrate the utility of beta-cyclohomocitral, the product of the process of our invention. It will be understood that these examples are illustrative and the invention is to be considered restricted thereto only as indicated in the appended claims.